Fairchild SEMICONDUCTOR RC5040 Hardware User Manual Download Page 18 | Manualshive

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AN42

APPLICATION NOTE

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Summary of Contents for SEMICONDUCTOR RC5040

Page 1: ...In a high volume production envi ronment such as with personal computers however a CPU voltage change requires a CPU board re design to accommo date the new voltage requirement The integrated 4 bit D...

Page 2: ...r must be greater than 80 at high current draw and greater than 40 at low current draw Processor Voltage Identification The Pentium Pro package has four voltage identification pins VID3 VID0 that can...

Page 3: ...cally thus opti mizing efficiency under all loads The key differences between the RC5040 and RC5042 are listed in Table 4 Table 4 RC5040 and RC5042 Differences Refer to the RC5040 Block Diagram illust...

Page 4: ...0mV increments To guarantee stable operation under all loads a 10K pull up resistor and 0 1 F of decoupling capacitance should be connected to the VREF pin No load should be imposed on this pin Power...

Page 5: ...ripple current flowing through the output inductor allowing the use of a larger inductor value Operation at lower fre quencies increases the amount of energy storage that the bulk output capacitors mu...

Page 6: ...65 AP42 04 R7 10K C1 1000 F C2 C3 1000 F 1000 F C5 0 1 F DS2 1N5817 C12 1 F L1 1 3 H M1 2SK1388 M2 2SK1388 C8 C9 0 1 F 0 1 F RSENSE 8m 1500 F C13 L2 2 6 H M3 2SK1388 VREF C15 C14 1500 F 1500 F C4 0 1...

Page 7: ...5 TO 220 JA 62 5 NDP606AL TJ 125 C 33 40 JC 1 5 Motorola VGS 5V ID 37 5A TJ 25 C 6 9 TO 263 JA 62 5 MTB75N03HDL TJ 125 C 9 3 14 D2 PAK JC 1 0 Int Rectifier VGS 5V ID 31A TJ 25 C 28 TO 220 JA 62 5 IRLZ...

Page 8: ...re 7 illustrates how an external 12V source can be used to bias VCCQP A 47 resistor is used to limit the transient current into the VCCQP pin and a 1 F capacitor filter is used to filter the VCCQP sup...

Page 9: ...gate charge and f is the switching frequency Efficiency POUT pIN IOUT VOUT IOUT VOUT PLOSS PLOSS PDMOSFET PDINDUCTOR PDRSENSE PDGATE PDDIODE PDTRAN PDCAP PDIC 1 PDMOSFET IOUT 2 RDS ON DutyCycle DutyCy...

Page 10: ...rs This methodology limits the power delivered to the load during an overcurrent condition The voltage drop cre ated by the output current flowing across a sense resistor is presented to one terminal...

Page 11: ...037 0 5 1 650 10 3 1 048A RSENSE Vth min ISC 1 TF Vth min 1 0 ILoad max 1 TF Table 7 Comparison of Sense Resistors Refer to Appendix A for Directory of component suppliers Description Motherboard Tra...

Page 12: ...ue where R20 is the resistance at 20 C 20 0 00393 C T is the operating temperature andR is the desired value For temperature T 50 C the R change 12 Table 9 is a summary of tolerances for the Embedded...

Page 13: ...he output voltage as the load regulation col lapses into the short circuit control mode The output voltage does not return to its nominal value until the output short cir cuit current is reduced to wi...

Page 14: ...the Schottky diode is not being over stressed during a short circuit condition Schottky Diode Selection The application circuits of Figures 3 4 and 5 show two Schottky diodes DS1 and DS2 In synchronou...

Page 15: ...ity output voltage ripple and load transient response The calcu lation is as follows where V is the maximum voltage deviation due to load transients T is the reaction time of the power source and IO i...

Page 16: ...for the MOSFETs In general noisy switching lines should be kept away from the quiet analog section of the RC5040 That is traces that connect to pins 12 and 13 HIDRV and VCCQP should be kept far away...

Page 17: ...le and Silk Screen are presented below The actual PCAD Gerber File can be obtained from Raytheon Electronics Semicon ductor Division s Marketing Department at 415 966 7819 Figure 16 Example of Proper...

Page 18: ...AN42 APPLICATION NOTE 18...

Page 19: ...d at 1A increments an active load HP6060B or equivalent is suggested 6 In case of poor regulation refer to the procedures in the Troubleshooting section Troubleshooting 1 If no voltage is registered a...

Page 20: ...overshoots then the noise may cause the converter to function improperly 9 Next look at the HIDRV pin This pin directly drives the gate of the FET It should provide a gate drive Vgs of about 5V when t...

Page 21: ...th the supply However with the input filter design the Input Rush Current will be well within specification VID Iload A Vout V 1010 0 5 2 505 1 0 2 504 2 0 2 501 3 0 2 496 4 0 2 493 5 0 2 493 6 0 2 49...

Page 22: ...evice Description Case Temperature C Iload 9 9A Case Temperature C Iload 12 4A Case Temperature C Iload 13 9A Q3A MOSFET K1388 57 63 56 3 Q3B MOSFET K1388 58 64 66 6 L1 Inductor Unknown 53 56 61 2 Q2...

Page 23: ...design considerationsn and component selec tions layout guidelines and considerations guidelines for debugging and performance evaluations RC5040 RC5042 Evaluation Board Raytheon Electronics provides...

Page 24: ...00 Fax 852 2314 0061 National Semiconductor Japan Ltd Tel 81 3 5620 6175 Fax 81 3 5620 6179 Appendix A Directory of Component Suppliers Dale Electronics Inc E Hwy 50 PO Box 180 Yankton SD 57078 0180 P...

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